The past two decades have seen a growing interest in developing all-organic light-emitting devices as alternatives to inorganic based systems. The advantages of organic small molecules and light-emitting polymers for these devices include lower synthesis costs of the materials as well as the devices. In addition, most organic light emitting diode (OLED) materials have been shown amenable to large scale-up and provide high efficiency output. In 1987, researchers at Kodak developed OLEDs based on small organic molecules (see, e.g., U.S. Pat. No. 4,720,432 to Van Slyke, et al.); however, formation methods required an expensive vacuum deposition process. In the early 1990s, polymer based LED (PLED) devices were developed employing a π-conjugated poly(phenylene vinylene) polymer (see, e.g., U.S. Pat. No. 5,247,190 to Friend, et al.).
Despite the many advantages to using small molecules and polymers for OLEDs, the ability to create devices with distinct emissions over a broad range of wavelengths has required difficult and lengthy synthetic protocols or complex device fabrication techniques unfavorable for large scale-up and low manufacturing costs.
An alternative to the use of small molecules and π-conjugated polymers has been explored through creation of multi-layer emissive materials that contain both a hole and an electron transport component which have been doped with an electroluminescent (EL) dye (Jiang, et al., Chem. Mater., 12:2542, 2000). For single colored emission, these systems have shown promise in thin film devices. However, independent EL dye emissions from a polymeric film containing several EL dyes remains problematic due to documented energy transfer processes which can occur between proximal dye molecules.
What is needed in the art are PLEDs that can successfully incorporate multiple EL dyes so as to provide color-tailorable PLEDs that can effectively emit a wider variety of colors, including white light.